1. Field of the Invention
The present invention relates to a pen-type handwriting input device for detecting and recognizing handwritten information such as handwritten characters and symbols or for feeding such handwritten information to a computer or the like.
2. Description of the Prior Art
As input devices for feeding information to a computer, keyboards, mice, and data tablets are already in wide use. To realize pen-type input devices that do not require a tablet and thus afford higher portability, various proposals have been made to date. For example, according to some proposals, an input device detects its own movement during writing by means of an acceleration sensor provided inside the device and thereby feeds handwritten information to a computer for processing (Japanese Laid-Open-Patent Applications Nos. H4-195321, H4-256009, H7-110737, H8-076914, etc.); according to other proposals, an input device detects the pressure applied to a pen by the individual fingers of the user during writing (Japanese Laid-Open Patent Application No. H6-095800, etc.); according to still other proposals, an input device reads handwriting optically by means of an optical sensor (Japanese Laid-Open Patent Application No. H5-278390, etc.).
However, in a pen-type handwriting input device that is sufficiently portable and at the same time capable of detecting and recognizing handwritten information such as handwritten characters and symbols as written in reality or capable of feeding such handwritten information to a computer or the like, the movement of the pen itself during ordinary writing is too subtle to be fed effectively to an acceleration sensor as mentioned above. Of course, it is possible to electrically boost the acceleration signal, but such boosting ends in boosting noise as well, and thus does not make any easier the extraction of necessary signal components.
In particular, the detection of static acceleration is often simply impossible with some types of small-size acceleration sensors. The use of an acceleration sensor makes it necessary to align the x and y axes of the acceleration sensor precisely with respect to the direction of the stem of the pen as it is when the pen is held in writing position, and also to detect the up/down and other movement of the pen. This requires the use of a plurality of additional sensors and switches apart from the acceleration sensor itself, and thus inevitably makes the system and device as a whole unduly large.
To overcome this inconvenience, a proposal has been made according to which, in combination with an acceleration sensor, a capacitance-type pressure sensor is used that is fitted directly to a stick serving as the above-mentioned stem of the pen (Japanese Laid-Open Patent Applications Nos. H9-16320, H9-16321, H9-16322, etc.). However, according to this proposal, the detection of subtle movement of the tip of the pen is possible only by the use of a large-scale boosting circuit, and such detection, even if possible, is difficult to conduct especially when considerably strong pressure is applied to the pen.
Moreover, this structure suffers from susceptibility to noise, from large deviations that appear in the sensor output depending on the direction in which the pen is held during writing, and from great difficulty in returning the stem of the pen and the sensor to their origins and in correcting the zero-point output when the pen is not in use for writing, that is, when the tip of the pen is receiving no load.
On the other hand, an input device of the type that detects the pressure of the fingers suffers from noise greater than the actually needed signal components carrying handwritten information and requires extra detection of the up/down movement of the pen. An input device of the type that reads handwriting optically by means of an optical sensor needs to be capable of processing image data and thus cannot be realized without making the system and device as a whole unduly large.